As illustrated in FIG. 5, a steering apparatus for vehicle is constructed so that the rotation of a steering wheel 1 is transmitted by way of a steering shaft 5, a universal joint 7, an intermediate shaft 8 and a universal joint 9 to an input shaft 3 of a steering gear unit 2; and as the input shaft 3 rotates, a pair of left and right tie rods 4 are pushed and pulled, which applies a steering angle to the front wheels. With the steering shaft 5 inserted in the axial direction through a cylindrical steering column 6, the steering column 6, which is supported by the vehicle body, supports the steering shaft 5 so as to be able to rotate freely. In the example illustrated in the figure, an electric power steering apparatus is assembled, and an electric motor 10, which is an auxiliary power supply, is supported by a housing that is fastened to the front-end section of the steering column 6.
A tilt mechanism for adjusting the height position of the steering wheel 1 according to the size and driving posture of the driver is assembled in a steering apparatus for vehicle. The construction of a steering apparatus provided with a tilt mechanism has been disclosed, for example, in JP 2009-227181 (A), JP 2010-254159 (A) and JP 2011-121443 (A). In the conventional construction illustrated in FIG. 5, the front-end section of the top of the housing 11 is supported by the vehicle body 12 by way of a tilt shaft 13 that is arranged in the width direction of the vehicle body 12 so as to be able to pivotally displace. Moreover, in the portion near the rear end of the middle section in the axial direction of the steering column 6, a support bracket 14 is equipped that is supported by the vehicle body 12 and that comprises a pair of support plate sections 15 that are separated in the width direction. The portion near the rear end of the middle section in the axial direction of the steering column 6 is held on both sides in the width direction by the pair of support plate sections 15, and in that state, is supported by the vehicle body 12 by way of the support bracket 14. A displacement bracket 16 is provided in a portion on the bottom surface of the middle section in the axial direction of the steering column 6 that is held by the pair of support plate sections 15.
Long holes 17 that extend in the up-down direction in an arc shape that is centered around the tilt shaft 13 are formed in both of the pair of support plate sections 15. Moreover, a through hole 18 is formed in a portion of the displacement bracket 16 that is aligned with part of the long holes 17. In the construction illustrated in FIG. 5, a tilt and telescopic mechanism that is able to adjust the forward-backward position in addition to the up-down position of the steering wheel 1 is assembled, so the through hole 18 is formed as a long hole that extends in the axial direction of the steering shaft 5 and steering column 6. Accordingly, the steering shaft 5 and steering column 6 comprise expandable and contractible construction.
FIG. 6 and FIG. 7 illustrate a tilt steering column device that is assembled in a steering apparatus comprising a tilt and telescopic mechanism having the construction disclosed in JP 2011-214698 (A). In this tilt steering column device, the steering column 6 is constructed such that the front-end section of an outer column 19 that is arranged on the rear side fits with the rear-end section of an inner column 20 that is arranged on the front side so as to be able to slide and so that the entire length can be expanded or contracted. The outer column 19 is manufactured by die-cast formation of a light metal alloy, for example, and a slit 21 is provided on the front end thereof so that the inner diameter of the outer column 19 can elastically expand or contract. A pair of held plate sections 22 that forms a displacement bracket 16 is provided in portions that are on both sides in the width direction of the slit 21. Through holes 18 are formed in the held plate sections 22 as long holes that extend in the forward-backward direction. A support bracket 14 comprises a top plate section 34 that is arranged above the steering column 6 and a pair of support plate sections 15 that are bent at right angles downward from both end sections in the width direction of the top plate section 34. Long holes 17 that extend in the up-down direction and have a partial arc shape that is centered around a tilt shaft 1 (see FIG. 5) are formed in the pair of support plate sections 15. A tilt rod member 23 such as a tilt bolt, a push-pull rod or the like is inserted in the width direction through the long holes 17 and through holes 18. The support bracket 14 is supported by a vehicle-side bracket 36, which is fastened to and supported by the vehicle body 12 (see FIG. 5), by way of a fastening member 35 that is welded and fastened to the top surface of the top plate section 34.
An adjustment lever 24, which is a tilt lever, is provided on one end section in the axial direction of the tilt rod member 23, an anchor section 25 is provided on the other end section in the axial direction of the tilt rod member 23, and a cam apparatus 26 is provided in the portion near one end of the middle section in the axial direction of the tilt rod member 23. With this kind of construction, a tilt-lock mechanism is formed that expands or contracts a space between the inside surfaces of the pair of support plate sections 15 based on the pivotal movement of the adjustment lever 24. The anchor section 25 has a circular plate shape such as the head of a bolt as a whole, and a first engagement convex section 27 is formed on the inside surface thereof. The first engagement convex section 27 engages with one of the long holes 17 (right hole in FIG. 7) and is able to displace only along the long hole 17. Therefore, the tilt rod member 23 is able to raise and lower along the long holes 17, but is unable to rotate around the axis thereof.
The cam apparatus 26 comprises a combination of a drive-side cam 28 and a driven-side cam 29 that functions as a pushing member. The drive-side cam 28 and the driven-side cam 29 are both formed entirely into a circular ring shape, and have center holes through which the tilt rod member 23 passes. The surfaces of the drive-side cam 28 and the driven-side cam 29 that face each other form cam surfaces (drive-side cam surface and driven-side cam surface) that are uneven in the circumferential direction. A second engagement convex section 30 is formed on the inside surface of the driven-side cam 29, and this second engagement convex section 30 engages with the other long hole 17 (left hole in FIG. 7) so as to be able to displace only along this long hole 17. Therefore, the driven-side cam 29 can be raised and lowered along the long hole 17, however, is unable to rotate around the axis thereof. Here, the “inside surface” is defined as the side surface that is near the center in the width direction of the steering column 6, and the “outside surface” is defined as the side surface that is near the outside in the width direction of the steering column 6. The drive-side cam 28 is joined and fastened to the base-end section of the adjustment lever 24, and is such that as the adjustment lever swings in reciprocation, the drive-side cam 28 rotates in reciprocation around the tilt rod member 23. A thrust bearing 32 is provided between the nut 31 that is screwed onto the other-end section of the tilt rod member 23 and the outside surface of the base-end section of the adjustment lever 24; and this thrust bearing 32 makes it possible for the drive-side cam 28 to pivot in reciprocation, while at the same time supports thrust loads that act on the drive-side cam 28. The nut 31 is prevented from becoming loose by crimping or the like.
When adjusting the position of the steering wheel 1, the dimension in the axial direction of the cam apparatus 26 is reduced, and the space between the driven-side cam 29 and the anchor section 25 is widened by pivotally moving the adjustment lever 24 in a specified direction (generally, downward). As a result, the surface pressure at the areas of contact between the inside surfaces of the pair of support plate sections 15 and the outside surfaces of the held plate sections 22 is decreased or lost, and the inner diameter of the front-end section of the outer column 19 is elastically expanded, and the surface pressure at the area of contact between the inner-circumferential surface of the front-end section of the outer column 19 and the outer-circumferential surface of the rear-end section of the inner column 20 is decreased. In this state, the up-down position and forward-backward position of the steering wheel 1 can be adjusted within the range that the tilt rod member 23 is able to move in the long holes 17 and through holes 18. After the steering wheel 1 has been moved to a desired position, by pivotally moving the adjustment lever 14 in the opposite direction (normally upward), the dimension in the axial direction of the cam apparatus 26 increases and the space between the inside surfaces of the support plate sections 15 is reduced, and as a result, the surface pressure at the areas of contact between the inside surfaces of the support plate sections 15 and the outside surfaces of the held plate sections 22 increases, the inner diameter of the front-end section of the outer column 19 elastically decreases, the surface pressure at the area of contact between the inner-circumferential surface of the front-end section of the outer column 19 and the outer-circumferential surface of the inner column 20 increases, and the steering wheel 1 is maintained at the adjusted position.
In addition to the mechanism illustrated in FIG. 6 and FIG. 7, various kinds of mechanisms are known that enable adjustment of the position of the steering wheel by adjusting the pressure force on the outside surfaces of a pair of support plate sections of a support bracket, or maintains the position of the steering wheel after adjustment. For example, a mechanism is known in which the tilt rod member is supported such that the tilt rod member can rotate around the center axis thereof. In this mechanism, a thrust bearing is provided between the anchor section 25 and outer surface of one of the support plate sections 15, and the base-end section of the adjustment lever 24 is joined and fastened to the other end section of the tilt rod member 23. Alternatively, construction is known in which the first engagement convex section 27 of the anchor section 25 engages with one of the long holes 17 so as to be able to displace only along the long hole 17, and the base-end section of the adjustment lever 24 is joined and fastened to a nut 31 that is screwed onto the other end section of the tilt rod member 23 and that functions as a pressure member. In this construction, by rotating the nut 31 with the adjustment lever 24, the space between the nut 31 and the anchor section 25 is increased or reduced.
In any construction, it is necessary that the engagement convex section be engaged with one of the long holes in at least one location so as to be able to displace along the long hole, and such that rotation centered around the tilt rod member is prevented. Moreover, in order to sufficiently ensure the force for keeping the steering wheel 1 in the adjusted position, it is necessary to maintain the surface pressure at the areas of contact between the inside surfaces of the pair of support plate sections 15 and the outside surfaces of the displacement bracket 16 after the space between the anchor section 25 and the pressure member such as the driven-side cam 29 has been reduced. In order to maintain the surface pressure at these areas of contact, it is necessary to definitely reduce the space of the portions of the pair of support plate sections 15 that hold the displacement bracket 16. As illustrated in FIG. 6 and FIG. 7, when the displacement bracket 16 is provided on the bottom side of the steering column 16, it is relatively easy to maintain the pressure at these areas of contact. The reason for this is that, even when the steering wheel 1 is positioned at the top end of the adjustment range, the portions of the pair of support plate sections 15 that hold the displacement bracket 16 are separated from the top ends of these support plate sections 15, and the moment that acts in a direction that brings the held portions closer to each other can be made to be relatively large.
On the other hand, in construction in which a displacement bracket is provided on the top side of the steering column, as disclosed in JP 2004-001562 (A), when the steering wheel is located on the top end of the adjustment range, it becomes difficult to ensure the surface pressure at the areas of contact between the inside surfaces of the pair of support plate sections and the outside surfaces of the displacement bracket. FIG. 8 to FIG. 10 illustrate an example of construction in which a displacement bracket 16a is provided on the top side of an outer column 19a of a steering column 6a. In this construction, the displacement bracket 16a does not protrude below the steering column 6a, so it is advantageous in improving the degree of freedom of design for protecting the knees of the operator during a collision accident.
However, when the steering wheel is positioned at the top end of the adjustment range, the displacement bracket 16a becomes located very close to the top-end section (base-end section) of the pair of support plate sections 15a of the support bracket 14a. When the space between the anchor section 25 and the driven-side cam 29 is reduced due to operation of the adjustment lever 24, the pair of support plate sections 15a displace around the respective top-end sections. The moment that acts on these support plate sections 15a becomes smaller toward the top-end sections of the support plate sections 15a, which are the centers of displacement of the support plate sections 15a. Therefore, in the construction illustrated in FIG. 8 to FIG. 10, when the trying to maintain the surface pressure at the areas of contact between the inside surfaces of the pair of support plate sections 15a and the outside surfaces of the displacement bracket 16a when the steering wheel is positioned at the top end of the adjustment range, the distance between the adjustment lever 24a and the top-end section of the pair of support plate sections 15a is short, and the moment that acts in a direction that would bring the support plate sections 15a closer to each other becomes small, so it is necessary to increase the operating force that is applied to the adjustment lever 24a. The large difference in the operating force for operating the adjustment lever 24 that occurs in this way due to the difference in the up-down position of the steering wheel 1 gives the operator that is operating the adjustment lever 24a an uncomfortable feeling, so is not desirable.
By employing construction in which the height dimension of the pair of support plate sections 15a is increased and it is possible to maintain the distance between the displacement bracket 16a and the top-end section of the support plate sections 15a even when the steering wheel 1 is positioned at the top end of the adjustment range, it is possible to lessen this uncomfortable feeling. However, in this construction, as long as the height of the portion on the vehicle body side where the support bracket 14a is assembled is the same, the installation position of the steering column 6a will be located further toward the bottom side, so except for cases in which there is plenty of installation space for the steering column device, employing this construction is difficult.
In the case of the construction disclosed in JP 2004-001562 (A), the top-half sections of the inside surfaces of the anchor section and driven-side cam are recessed when compared with the bottom-half sections thereof, or the portions around the top-end section of the long holes on the outside surfaces of the support plate sections are recessed. However, in the former construction, the assembly direction of the anchor section and the driven-side cam is limited, so the efficiency of the assembly work is lowered. On the other hand, in the case of the latter construction, not only does it become necessary to perform an extra process such as a surface pressing process for recessing the outside surfaces of the support plate sections, it also becomes necessary to perform a deburring process for removing burrs that occur during the pressing process, so the manufacturing cost increases.